Process for formation of non-abrasive refractory rubbing surface having high thermal conductivity by casting



Sept. 17, 1968 TAMEICHI IMAGAWA 3,

PROCESS FOR FORMATION OF-NON-ABRASIVE REFRACTORY RUBBING SURFACE HAVINGHIGH THERMAL CONDUCTIVITY BY CASTING Filed May 26, 1964 FIG.| FIG-2 FIG4 a) a 50- E a: I T 20 HR INVENTOR. TAMEICHI IMAGAWA :60 260 3'00 4'00560 oo W l I j ,7 TEMPERATURE 0 a-z/wh ETTORNEYS United States Patent3,401,736 PROCESS FOR FORMATION OF NON-ABRASIVE REFRACTORY RUBBINGSURFACE HAVING HIGH THERMAL CONDUCTIVITY BY CASTING Tameichi Imagawa,Omiya, Japan, assignor to Bridgestone Cycle Industry Company Limited,Tokyo, Japan, a corporation of Japan Filed May 26, 1964, Ser. No.370,282 Claims priority, application Japan, Aug. 27, 1963, 38/45,124;Oct. 22, 1063, 38/56,623 5 Claims. (Cl. 164-95) ABSTRACT OF THEDISCLOSURE A method of coatinga metal article having a layer ofnon-abrasive heat-resistant metal on a body of high thermal conductivitymetal comprises spraying a first porous layer of a lower melting pointmetal on a sand core, spraying a second porous layer of higher meltingpoint non-abrasive heat-resistant metal on the first layer, positioningthe core in a casting mold, and pouring molten high thermal conductivitymetal into the mold and over the core, the porosity of said layerspermitting venting of entrapped air and gases therethrough and providinga good bond between the body and the layers. After separating thecasting from the core, the first layer may be removed to expose thelayer of non-abrasive heat-resistant metal.

This invention relates to a process for the formation of a non-abrasiveand heat-resistant metal layer on a body formed of a substance havingrefractory surface having high thermal conductivity which is applicableto frictional surfaces of relatively moving machine parts, such, forinstance, as those of a high speed brake hub drum of vehicles orcylinder and piston of internal combustion engines.

The general object of the invention is to provide an improved process offorming a non-abrasive and heat resistant surface on a high thermalconductivity body of the relatively moving machine parts by casting.

A further object of the invention is to provide a very strong corecapable of enduring rough handling and heat shock.

The inside surface of a machine part such as a cylinder of an internalcombustion engine, in particular, an aluminum cylinder of an automobileor frictional surface of a brake evolving an extremely large amount ofheat when exposed to a high temperature condition, such as damping hubdrum must have a good heat resistance as well as a good thermalconductivity, otherwise, heat of friction is accumulated to causeover-heating, which results in an accident such as abrasion sticking ofthe frictional surface.

In carrying out the invention in one way, a light metal having a highthermal conductivity, such as aluminum or aluminum alloy, is used as abase material for the machine parts by casting using a core preparedfrom synthetic resin-coated casting sands for shell holding. At first, anon-abrasive and heat resistant metal layer is formed initially on theouter surface of the said core by spraying, and then the coated core isset in a casting mold and a melt of the above mentioned base material ispoured in the mold and bonded to the non-abrasive and heat resistantmetal layer, and the latter is transferred to the surface of the articlemade of the base metal.

In a further improvement according to the invention, prior to applying anon-abrasive and heat resistant layer wear resisting metal on the outersurface of the core by a metal spray, a low melting point metal oralloy, such Patented Sept. 17, 1968 ice as zinc aluminum, or an alloythereof is applied as a 1st layer on the outer surface of the said coreby metal spraying process, that is, by an electrically heated moltenmetal spraying process, and a non-abrasive and heat resistant metalwhich forms the frictional surface of the article is, as a 2nd layer,applied on the 1st layer by a molten metal spraying process by utilizingthe fine irregularities of the surface of the 1st layer as holdingmeans.

By using such a low melting point metal or alloy in the formation of the1st layer, the thermal shock applied to the core is very low since themelt spray of the lower melting point metal has a small heat capacity sothat the damage and the thermal deformation of the core can bepositively prevented without necessity of great skill and large care asin the case of the direct spraying of the nonabrasive and heat resistantmetal layer. Moreover, the core is reinforced such that it cansufliciently stand heat stress caused by the thermal shock at thespraying of metal for the 2nd layer and local heating by the metalspray, whereby the core is mechanically protected against rough handlingwhich frequently happens in mass production, and the surface state ofthe 1st layer is an extremely effective layer of fine particles forwelding of the 2nd layer by spraying, therefore, a desired metal can becoated as the 2nd layer easily with a uniform thickness and non-abrasiveand heat resistant metal and wear resisting layer can be easily formed.

A 3rd layer of aluminum is, if necessary, formed by the molten metalspray on the 2nd layer on the surface of the treated core andthe core isthen set in a casting mold. Then, a molten metal having high thermalconductivity such as aluminum or an aluminum alloy is poured in the moldand as the 2nd layer and the 3rd layer also have porous surfacestructures consisting of fine particles of spray metal, the poured basemetal is very firmly adhered to the 3rd layer, the boundary layer formsan uneven structure and the combining surface areas are enlarged, whichresults in'increasing the thermal conductivity between layers. Also,since the surface of the core is only covered by the metal spray layers,gases can be easily vented in case of casting through the porous layers.

By then breaking finally the core, the layer fused onto the outersurface of the core is formed on the surface of the cast product andbyremoving the 1st layer having a low melting point from thus obtainedsurface, the 2nd layer of the non-abrasive and heat resistant metallayer can be obtained for use as a non-abrasive surface.

For a better understanding of the invention reference is taken to theaccompanying drawings, in which,

FIG. 1 shows a cross-sectional view of \a core for casting light metalcylinder of an internal combustion engine by the method of theinvention;

FIG. 2 is a partial sectional view of for use in automobiles;

FIG. 3 shows a microscopic structure of non-abrasive and heat resistantmetal layer; and

FIG. 4 is a characteristic diagram wherein the hub drum according to theinvention is compared with a conventional hub drum and shows that thedecrease of hardness accompanied by the temperature rise of hub drum anda high performance can be expected over a wide temperature range.

Referring to FIG. 1, reference numeral 1 represents a baked coreprepared from synthetic resin-located casting sands for shell molding bya conventional means.

The core 1 has a substantial strength but is liable to be damaged ifviolently handled and is deformed if it is subject to a sudden thermalshock locally.

According to the invention, a low melting point metal or alloy such aszinc, aluminum or an alloy thereof is a brake hub drum applied on theouter surface of the core 1 by a metal spraying process, to form the 1stlayer 2. The core 1 is reinforced by the 1st layer 2 and its strength isincreased,

Preferred examples of compositions of aluminum alloys suitable as thebase material of the cylinder are shown in Table 2.

thereby enabling to resist even considerably violent han- TABLE 2 glingaICl succeeding mechanical working without being 5 Si Cu Fe Mg Mu Alamage Moreover, since the melting point of the (material used 8 2353 8EZ g 5312332 in the formation of the 1st layer 1s low and the heat ca-12. 00% 2. 0-4. 0% 1.5% 0. 30% 0. 02% Balance pacity necessary forinstant melting of the spraying material and that of the sprayed metalare small, the core 1 When the process of the invention is applied tothe 1s not sub ected to a large thermal shock as 1n the case making ofcylinders, there is an advantage that treat mefal Spraying f 1st l hencet 1st layer 2 ment similar to a so-called porous treatment in a chrolseaslly formed without causmg defofm'atlon' mium plated cylinder linercan be obtained inevitably 1 gf of the 1st layer 2 thls fixampla withoutany effort since the porous portions and recesses are impregnated withlubricant, and also the porous por- The core 1 remfofced by the 1stlayer 2 sufiiiclently 'tions form a vent passage for gases duringcasting, which endure the mechanical operation of a continuous meltimprove the quality of cast Product spraymg devlca As, in the process ofthe invention as mentioned above,

AS a Second Step rlon'abraslve' and l feslstant the 1st layer 2 of a lowmelting point alloy or metal is {natal s uch as Wear reslsung steel orwear reslstmg alloy first formed on the outer surface of the core 1 bymolten 1s apphed on the outer surface of the layer 2 by metal sprayingprocess and then the 2nd layer 3 of a P Spray to form a layer Asultalilefomposr non-abrasive and heat resistant material is formed onthe tion of steel as the material for the 2nd layer 15 illustratedSurface of the 1st layer 2 the damage and the deforma Table tion of thecore by external force, thermal shock 'and TABLE 1 heat stress caused bythe melt spray of the 2nd layer 3 Percent can be extremely reduced,which makes the mass produc- C tion of such a kind of casting operationpossible and Mn Q70 increases largely the production efiiciency. Also,the pres- P O'04 ence of the 1st layer 2 particularly facilitates theforma- S tion of the non-abrasive and heat resistant metal layer Fe98'42 as the 2nd layer 3 on the surface of [the core 1 and The thi k eof th 2 d layer 3 i 1 1,5 protects the core 1 from damage during thepouring time I thi case, lag th 2 d l e 3 i thoroughly i t of a moltenmetal thereon. In addition to serving as the ne t d b means f th porousuneven Surface f th 1 non-abrasive and heat resistant metal layer, thesecond layer 2, the former may have sufficient thickness and can a layeris strongly joined With the poured base metal, heat be well adhe ed tothe latt d as h h t f lt is effectively transferred from the 2nd layer 3to the base metal spray is not directly applied to the core 1 by thematerial through the intimately combined portion and the presence of the1st layer 2 having a high thermal conheat is p i iv ly r dia ed.ductivity, the damage and the thermal deformation of the Anotherembodiment f th inv ntion as applied to a core lc-an be positivelyprevented. brake hub drum of automobiles will be explained with Theabove molten metal spray process can be effecreference to FIG' 2 where 8designates a hub drum made tively applied to the case of casting a corehaving 3, Of aluminum or its alloy Shown in partial section, 9 iS itscomplicated shape as the core is sufficiently reinforced. Tim P 10 aflange, 11 is the Surface layer of a high Further, if necessary, alilght met l r a light alloy may heat resistant and non-abrasivematerial coated to the be a lied o th o ter rfa of th 2 d layer 3 b ainner peripheral surface of the rim 9, and 12 is an intermelt sprayprocess t f r 3 d layer 4, mediate layer of base material aluminum, thatis, which The thickness of the 3rd layer 4 may be about 0.5-1.0 firmlybonds alloy-like the Surface layer 11 to said Tim mm. for effectivelystrengthening weldability of a poured Portion made of base metal- 13represents a brake $1106, metal with the base material but in the caseof applying 14 a brake lininga heat-treatment as after-treatment todiffuse the base Examples of the composition of a heat resistant andmaterial into the material of the 2nd layer 3 and to form non-abrasivematerial which constitutes the surface an alloyed intermediate layer,the formation of such a hardening layer and of the aluminum alloy asdrum 3rd layer 4 is not always necessary. However, more commaterial areshown as in Tables 3 and 4.

TABLE 3 Chemical compositions, percent Sample Number 0 Mn Si P 8 Cr NiFe Hard- X1855 1. Chromium steeL- 0. 32 0.50 0. 05 0. 02 0. 02 13.585.14 HRc 20. 2. High carbon steel 0.8 0.70 0.04 0.04 98.42 HRc 36. 3.Ni-Cr-Mn steel." 0 04 2.00 0. 03 0. 03 1 5 4.00 HRc 25. 4. Mo steelalloy MoAbovc 09%. Re 38.

1 Mo 13%. 2 Remaining.

plete fusing or combination can be obtained by further applying theheat-treatment in the case of forming the 3rd layer 4 also.

The core 1 having thus sprayed layers is set in a casting mold formaking a cylinder and a melt 'of base metal is poured in the mold tocast the cylinder body containing the 2nd layer 3 and the 3rd layer 4.As the outer sprayed layer 5 of the core 1 has the fine porous unevensurface, the poured base material is interconnected with the sprayedlayer at the boundary and is combined strongly thereto.

TABLE 4 Chemical compositions, percent Sample N umber Si Mg Cu Mn Fe Al7. 54 0.33 0. 64 0. 02 0. 40 Remaining. 10.10 0.30 0.20 0.8 Do. 12.000.30 2. 0-4.0 O. 02 1. 5 D0.

According to the invention, the heat resistant and nonabrasive materialas mentioned in Table 3 is sprayed to a thickness of 0.5 to 1 mm. on thesurface of the shell molding core, which forms the inner periphery ofthe rim 9, to form the surface layer 11 (FIGS. 2 and 3) and anintermediate layer 12 of aluminum is sprayed thereon, the core is thenput in a casting mold, a melt of an alloy of base material asexemplified in Table 4 is cast by a diecasting or conventional castingprocess and the coated layers on the core surface are cast together inthe molten base metal or alloy.

In this case, the intermediate layer 12 of aluminum serves as a binderwhich fuses and firmly bonds the base material 16 and the surface layer11 and fills the fine gaps between the coating particles of surfacelayer 11 to adhere perfectly.

Since the thickness of the surface layer 11 is thin and the layer isbonded tightly by the intermediate layer 12 alloyed to the basematerial, the friction heat when produced is transmitted immediately tothe base material 16 to produce no substantial temperature differencebetween both layers and the thermal expansion of the surface layer 11 issubstantially equal to that of the base material 16. The friction heatgenerated on sliding contact surface of hub drum is thus immediatelydissipated without causing any trouble in the thin coated layer anddefects as in the previous method owing to the accumulation of heatwould never occur.

When the core is broken easily after casting the hub drum, the surfacelayer 11, which forms a brake sliding contact surface, appears, thesurface layer requires only a direct grinding processing without specialmachining operation and thus a hub drum of high performance can beproduced without the increase in operating steps.

What I claim is:

1. The method in accordance with claim 5 in which the nonabrasive andheat resistant metal coating comprises steel.

2. The method in accordance with claim 5 in which said lower meltingpoint metal is selected from the group consisting of zinc, aluminum andan alloy thereof.

3. The method in accordance with claim 5 in which said metal having ahigh thermal conductivity comprises aluminum alloy.

4. The method in accordance with claim 5 which includes the step ofapplying a coating of aluminum over said coating of nonabrasive and heatresistant metal.

5. The method for forming a non-abrasive and heat resistant surface on asurface of a body cast from material having high thermal conductivitycomprising the steps of forming a core from casting sand containing asynthetic resin binder to the desired shape and size and to define thesurface of said body cast over said core, coating at least said surfacedefining portion of said core by spraying thereon a lower melting pointmetal in the form of molten particles prior to and followed by coatingsaid sprayed surface with a porous layer of non-abrasive and heatresistant higher melting point metal by spraying said metal thereon inthe form of molten particles, positioning said core in a casting mold,pouring molten metal having a high thermal conductivity into said moldand over said core to cast said body, and during casting to vententrapped air and gases through said porous layer to permit said pouredmetal to penetrate into the interstices of said porous layer and to bondsaid metal of high thermal conductivity to said porous layer by saidpenetration, and separating said core from said cast body and leavingsaid cast body which is integrally bonded to said non-abrasive and heatresistant layer.

OTHER REFERENCES Metal Spraying and Sprayed Metals; Turner and Ballard,Journal of the Institute of Metals, No. 2, vol. XXXII, 1924, pp.296-297.

Iron and Steel; June 1963, pp. 308-312, Foundry Core Practice; Dietert,Harry W., 2nd ed., vol. 36. No. 7, 1950.

Published by the American Foundrymens Society, Chicago, pp, 1, 2, 107,174.

- I. SPENCER OVERHOLSER, Primary Examiner.

V. K. RISING, Assistant Examiner.

